Self-regulating drive for rotary abrasive tools



March 21, 1950 R, D, WATSQN 2,501,554

SELF-REGULATING DRIVE FOR ROTARY ABRASIVE TOOLS Filed Dec. 8, 1948 3 Sheets-Sheet 1 db W um 'March 21,1950 R R, D, WATSON 2,501,554

SELR-REGULATING DRIVE RoR ROTARY ABRAsIvR TooLs- Filed Dec. 8, 1948 5 sheets-sheet 2 March 2l, 1950 R. D. WATSON 2,501,554

, sELFREGULATING DRivE FOR ROTARY ABRAsIvE TooLs Filed Dec. 8, 1948 5 Sheets-Sheet 3 i Patented Mar. 2l, 1950 SELF-REGULATING naive Fon.

ABRAsIvE 'rooLs Watson, Westwood, Mass., as-

Robert Douglas normar signor of one-half to James Shapiro, Brookline,

Mass.

I Application December 8, 1948, Serial No. 64,181

l My invention relates to rotary tools employedfor grinding, sanding, or polishing surfaces. More particularly, my invention pertains to tools of the general portable type in which an abrasive or polishing disk is secured to an appropriately formed head arranged for rapid rotation.

Ordinarily a rotary sanding machine includes a circular pad secured to the shaft or spindle of the machine and provided with means for clamping a relatively stiff abrasive disk upon the outer surface of the pad or to the driving spindle. Although such clamping means are ideally suited for some operations, they do not allow the use of flexible coated abrasives, such as found in paper or cloth backings, except by the most expert users. Such backingsare less costly but relatively weaker than the commonly employed fibre backings and will rupture easily in use. Flexible sandpapers cannot be utilized with conventional rotary sanders, because they crumple and tear in response to the accidental and almost unavoidable applications of excess pressure of the disk upon the surface being treated.

The most important object of my invention is to achieve a self-regulating pressure responsive rotary sanding machine capable of use with ilexible paperor cloth coated abrasives in relatively unskilled hands.

Another object of my invention is to extend the range of usefulness of rotary finishing equipment.

A further object of my invention is lto improve the eiiiciency and economy with which surfaces may be prepared for final finishing.

An important. feature of the invention resides in the combination of an abrasive member, a pad, and means responsive to the drag of the abrasive upon the work surface for stopping .or slowing'down the rotation of the abrasive member when the drag exceedsia predetermined value below the point at which the member will rupture.

Another feature of the invention resides in the v combination of a resilient pad, an abrasive sheet, and means for securing the sheet to the pad in such fashion that an excessive drag upon the sheet will be sufficient to stop or slow it.

Stili another feature of the invention resides in the combination of a pile fabric pad and means for locating an abrasive sheet in frictional engagement with the pad in such fashion that the pile flattens as the result of centrifugal force, r

leaving the abrasive sheet free to stop or decrease in speed when its pressure, or drag, upon a work surface exceeds a certain amount.

My invention is based in part upon the concept that an abrasive sheet may be rotated not in 1o claims. (ci. 51-197)v conventional fashion by being tightly clamped at its center to a driving spindle but rather by frictional engagement between an extensive portion of the area. of the back of the abrasive sheet and the front of the pad.. The amount of driving force thus obtained may easily be regulated. If the friction grip of the sheet upon the pad be exceeded bythe drag of the sheet upon a Work surface, the sheet will slow down or stop completely. However, the stresses then engendered in the sheet must be less than sufficient to rupture the sheet. Otherwise an excessive drag upon the sheet will rupture it before the point is reached at which the turning of the sheet is slowed or stopped. In other words the sheet drive is self-regulating.

These and other objects and features of the invention will be more readily understood and appreciated from the following detailed description of preferred embodiments selected for purposes of illustration and shown in the accompanying drawings, in which: .y

Fig. 1 is a view in side elevation of the head of a rotary sanding machine embodying the invention,

Fig. 2 is a view in cross section along the line 2 2 of Fig. 1,

Fig. 3 is a view similar to Fig. 2 lbut illustrating lthe relation of the elements in motion, l e

Fig. 4 is an exploded view in cross section through the adjustable slip nut and associated elements,

Fig. 5 is a view in side elevation showing the application of a sander constructed in accordance with the invention for work upon a curved surface,

Fig. 6 is a view in cross section through a sander head illustratingv another embodiment of the invention,

Fig. 7 is an exploded view in cross section through the elements of the slip-*nut employed in the embodiment of Fig. 6, y

Fig. 8 is a view incross section through a sander head showing a third embodiment of the' through the friction drive elements of the embodiment shown in Fig. 13, and

Fig. 14 is a plan view of the distorted drive washer. The present application is a continuation-inpart of my copending application Ser; No. 45,801, filed August 24, 1948.

For reasons which will later appear, I regard the embodiment disclosed in Figs. 1-5 as the best mode now known to me for practicing my invention. In Figs. l and 3 I have suggested at I0 the housing or casing of a conventional rotary sander in which a motor (not shown) drives a spindle I2 through bevel gears (also not shown) the details of the drive for the spindle are not important and vary somewhat among the models currently on the market. Ordinarily the spindle is made to .turn within the range of from 1300-5500 R. P. M.

The end of the spindle I2 is externally threaded as shown in Fig. 2 to receive a domed hub Il merging with a substantially dat, circular backing plate I6. 'Ihe hub and backing plate may conveniently be cast as one piece of relatively light metal such as aluminum, although other constructions will suggest themselves. For example a plywood annulus may be securedto a metal hub. As shown, the hub I4 is internally threaded and should be firmly screwed on the threaded end of the shaft or spindle I2; however, the manner in which the hub is secured to the shaft is not at all critical.

Secured to the backing plate I6 is a centrally apertured disk or sheet i8 of webbing, duck, vulcanized rubber or the like, preferably firmly cemented in place. A layer of latex 20 is spread on the front surface of the sheet I8 to serve as a matrix for the looped ends of a pile 22 of wool yarn or the like'anchored by conventional stitching 2l. The pile is relatively heavy and on a new pad may extend an inch or more from the surface of the sheet I8. The details of a suitable form of pad are disclosed in United States Letters Patent No. 2,366,877. From what has been said it follows that the pad (generally denoted by the reference character 2l) is secured to the backing plate and hub and therefore turns with the spindle I2.

For locating an abrasive sheet upon the pa 2| I provide a slip nut assembly including a cylindrical internally threaded member or nut 30 externally flanged at its outer vend to fit within a counterbore in the head of a bushing 32 anged at its outer end to form a clamp or pressure plate. Received in the member 30 is a set screw 34. The member 30 is slipped through the bushing 32, on which it turns freely, and screwed on the spindle 'I2 as far as the setting of the set screw will allow, and it will be evident that the set screw may be moved in and out to determine the axial position of the members 30 and 32 upon the spindle. Alternatively a jam nut could be threaded on'the spindle I2 ahead of the barrel nut 32, butthe set screw is a more convenient arrangement.

A thin flexible disk 38 of coated abrasive such as sandpaper, emery cloth, or the like, is pro-- vided with'a central hole just large enough to fit over the barrel of the bushing 32 and be caught under its iiange. It should be noted that the bushing is iilleted beneath the i'lange as indicated at 33 not only to provide added strength to the bushing but also to deform the edges of the hole in the abrasive disk and conform it to the shape of the bushing, thus providing a relatively broad '4 area of frictional contact between the disk and thebushing. v

As the nut is screwed on the shaft I2, the broad iiange of the bushing 32 engages the central area of the disk 3S, locating it accurately and bringing it into frictional engagement with the surface of the pile pad 2I. The resulting compression upon the center of the disk will cause it to assume a somewhat wrinkled conical shape as shown in Fig. 2. The amount or extent of frictional engagement between the back of the disk and the face of the pad is regulated by the position of the set screw 34.

When the motor is switched on, the pad and disk turn at high speed. Centrifugal force and the turning moment of the assembly cause the individual piles to lie outwardly and rearwardly with respect to the direction of rotation. The result, as shown in Fig. 3, is to flatten out the entire pad; in consequence the disk also flattens out and loses substantially all of its wrinkles. The flattening of the pad diminishes to some extent the frictional engagement of thepad and the disk, and the latter may be regarded as almost iioating on the pad. Since the bushing 32 turns freely on the nut 30, the drive to the fore the drag of the work on the disk overcomes disk and to the bushing is obtained by the drag of the disk on the pad. If, now, the disk 36 is held against a work surface to grind or smooth it, the drag of the disk on the work will vary directly with the pressure applied by the operator.

The application of pressure beyond a certain amount will increase the drag of the disk on the work until it equals or exceeds the drag of the diskion the pad. Then the disk will slow down and stop, the bushing then also stopping with it. When the operator relaxes the pressure, the friction of the pad on the disk will again exceed that of the disk on the work, and the disk will spin again.

If the set screw 34 is set too far in, the grip of the pad on the disk will be too small; conversely, if the set screw is set too far out, the disk will be clamped securely against the pad and rupture bethe drag of the pad on the disk. The limiting factor is the toughness of the disk since the stopping force must be applied through it. We may therefore draw the conclusion that the driving force exerted by the pad on the disk and the drag of the work on the disk must both be less than the force required to crumple and rupture the disk.

The device of my invention is selfregulating and automatic, in the sense that the disk is so assembled on the pad that slippage occurs solely in response to the amount of drag between the disk and the work; tlie other variables are preset by the adjustment of the set screw.

While the form of pad shown in Figs. 1 5 is preferable because its flattening action facilitates a more delicately responsive setting of the device, I do not limit the invention to the form shown. However, the thick resilient pad greatly improves the action of the sander on curved surfaces, as shown in Fig. 5. The pad flexes easily and permits the conformation of the disk to the surface to be' treated; at the same time the device will operate equally as well, stopping easily if the drag or pressure exceeds the safe limit.

In Figs. 6 and 7 I have shown another embodiment of myl invention. Here I utilize a hub 40 screwed On the Sauder spindle 42 and terminating in'a flat circular flange or plate 44 of relatively small diameter. A solid pad 4.6 of relatively soft resilient rubber, felt, or the like is lshaft 42. As before, a thin flexible sandpaper disk 56 isslipped over the bushing 58 and held in place, by the flange 52, upon the surface voi' the pad 46. It will be observed -that this construction affords slippage in two locations; thev pad 46 slips upon the hug flange 44, and the disk 56 slips upon the pad. Although in my copending application, the only slippage described is that of the pad upon the hub flange, I have found that in actual practice the application of excess pressure on the work will rst operate to stop the disk 56 and only after that to stop the pad itself. While I had successfully operated the device shown in Fig. 6, I had not appreciated the fact that slippage of the disk upon the pad was inherent in the construction. the stopping of the pad itself being more strikingly evident. Exhaustive tests, however, haveconclusively shown that the disk slips first.

In Figs. 8 and 9 the construction shown in the same as in Figs. 6 and 7, with the exception that the bushing is eliminated and the nut provided with a broader flange. As before, a flanged hub 68 is screwed on the sander shaft 62. a solid pad 64 is slipped over the shaft, and an abrasive disk 66 is laid upon the surface of the pad. The nut comprises a, flanged head 18, and a cylindrical barrel 88 in which a set screw is threaded. It will be noted that in this form the abrasive disk will turn upon the nut as it stops. a factor tending. rapidly to erode the nut. The form shown is therefore less costly to manufacture than the other constructions illustrated but is subject to the disadvantage that its life in action is much shorter.

In Figs. and 11 a fourth embodiment of the invention -is illustrated. Here I incorporate a spring loaded slip clutch in the drive for the pad, disk, and backing plate. The end of the sander shaft '|8 is tapped to receive a bolt 12 employed to clamp a metal disk 14 securely upon the end of the shaft 18. A cylindrical bushing 16 is held between the disk `|4 and a shoulder formed on the shaft '|8, whilea cup-shaped nut 'I8 fitsv over the bushing '|6 and is shouldered to bear upon the surface of the disk 14. Cooperating with the nut T8 is a hub member 88 having a threaded barrel engaging the nut, while a. compression spring 82 is disposed within the barrel to bear upon the disk 14. The hub 88 is provided With an integral circular plate 84 to which is cemented a resilient circular pad 86. A broad-A headed screw 88 serves to clamp an abrasive disk v 88 securely and in flat condition upon the surface of the pad 86. The drive for the nut 18, hub 88, pad 86, and disk 98 is transmitted solely through the frictional contact between the metal disk 'I4 vand the shoulder of the nut 18. When thepressure exerted on a Work surface is sufllcient to overcome that exerted by the spring 82,

the disk 'i4 separates from the shoulder of thev nut 18 and everything stops except the shaft and the' metal disk. Here againthe device is selfregulating in response to the drag or pressure exerted by the operator against the work surface. By adjusting the hub 88 in and out of the nut 18, the pressure of the spring 82 is varied, thus providing means for adjusting the effective pressure at which rotation of the abrasive member is stopped. To preserve the adjustment a check nut v92 is threaded on the barrel of the hub 88, the relative positions of the hub and nut 18. One other embodiment of the invention is shown in Figs. 'l2-14. Here I utilize a hub |88 l which lits loosely over a bushingon the sander shaft |82 and rests against a shouldercut in the shaft. 'I'he hub |88 merges smoothly into a flat circular backing plate |84 and is chambered centrally about the shaft 82. Secured to the backing plate |84 is a resilient circular rubber pad |86 of the usual type, and a flanged cylindrical nut |88 is threaded upon the shaft |82 to an extent determined by the axial position of a set screw H8 operating in the barrel of the nut. The

' flanged head of the nut |88 serves to clamp an abrasive disk 2 fast upon the surface of the pad |86, in flat condition.

In the central chamber of the hub |88 there is placed a distorted spring steel annulus or washer I4 bearing at one side upon the huband at the other side upon a retaining washer ||6 composed of a porous metal impregnated with a lubricant. A split ring ||8 contained in a groove in the hub chamber serves to retain the Washers ||6 and.

||4 in place. The inner end of the nut |88 is reduced to fit through the split ring ||8 and bear against the washer ||6.' The pressure of the nut against the Washers ||4 and 6 is a function of the adjustment of the set screw ||8 and compresses the distorted spring washer ||4 to .a certain extent. The nut |88 turns with the shaft |82 and drives the hub |88 through the frictional contact of both members upon the washer ||4.` .When the drag of the abrasive disk ||2 upon a work surface exceeds the drag of the hub |88 on the washer ||4, the assembly of the hub, pad, and abrasive disk will cease rotating. The amount of drag suilicient to stop the assembly will depend upon the adjustment of the nut on the shaft |82 as fixed by the axial position of the set screw I8. i

It will be observed that all the embodiments shown include means responsive to drag on the abrasive disk for stopping the disk and that the value of the effective drag is subject to adjustment. Furthermore, forV successful operation in each case, thefriction grip elements must be engaged to driveJ or grip at pressures less than the drag suilicient to crumple and rupture the disk. Also, in each ease the device is adjustable to compensate for changes in dimensions of the parts resulting from wear. The thickness of the pads Vwill diminish with wear and require corresponding changes in the axial positions of the set screws.

Although all the several embodiments will operate successfully, I prefer to employ the structure shown in Figs. 1-5, as previously stated. In that embodiment only the very thin, light abrasive disk is stopped while the other elements continue to rotate. The mass of the disk is negligible, hence this construction facilitates the most delicately responsive operation of the sander. Where the pad or pad and hub also are stopped, a more considerable mass must'be dealt with. The momentum of the greater mass, in accordance with the relation f=mv, tends to continue rotation; the dra'g on the disk be greater than that required merely to stop the disk by is' one element in a friction drive, while the other element comprises the back face of the Yabrasive disk itself. Abrasive disks of the type herein shown consist, in effect, of two layers: a layer of abrasive granules in an adhesive matrix,

lngiyconnected to the pad and backing plate Qfrbyaslip clutch comprising a member ,having a and a backing sheet of paper, cloth, nbre, or combinations thereof.

While I have referred to abrasive disks and sanding machines, I do not exclude from my invention equipment designed for polishing, grinding or other surface treating operations.

In essence the invention comprises a friction grip element of elements interposed mechanically between the disk and the shaft of the sanding machine. Various modifications of the devices herein shown will suggest themselves to those skilled in the art, but the invention is to be measured by the language of the appended claims and not limited to the specific details shown and described.

Having thus disclosed my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. In combinationwith a tool including a threaded spindle, a pad secured to said spindle and an abrasive disk overlying said pad, a diskmounting attachment comprising an annular flanged sleeve threaded to the spindle, a clamp engaged by the flange on the sleeve and surrounding said sleeve and adapted to bear on said disk, and means for locking the sleeve in adjusted position on the spindle.

2. A self-regulating friction drive device for rotary sanding machines including a threaded spindle, comprising a resilient pad secured on Vsaid spindle against relative rotation therewith,

a pressure plate, a threaded member engaging said plate and threadably connected to said spindle, and means for locking said threaded member to said spindle in predetermined position, whereby an abrasive disk may be frictionally engaged between said pad and said plate under selected pressure determined by the adjustment of said threaded member.

3. In combination with a sanding machine having a rotatable shaft and employing an abrasive disk; a friction drive mechanism comprising about a limited degree of frictional contact bea hub axially movable and freely rotatable on of the disk may overcome the spring and causeA the shoulder and element to slip relative to each other, thereby reducing driving torque from said hub, pad and disk.

4. A sanding attachment for operation with a shaft, comprising a backing plate removably attached to the shaft, a flexible centrally apertured disk pad concentrically attached to the backing plate, a centrally apertured exibie clamping flange adapted to press the central portion of the abrasive disk against the pad, screw threaded connecting means to connect the clamping member to the backing plate, said member being journaleg on a part of the screw threaded connecting means for rotation thereon when the friction between the abrasive disk and the work is suflicient to overcome the friction betweenthe member and the screw. threaded connecting means and means forlocking the connecting means and backing plate in fixed relationship. 5. A self-regulating frictional drive for abrasive disks employed in combination with a sanding machine having-a rotatable shaft, comprising a flexible pile fabric pad, a hub secured to said pad and threadably engaging the shaft of the sanding machine, an annular flanged bushing adapted to locate an abrasive disk upon the face of said pile pad, and coupling means rotatably mounted Within said bushing and flanged to engage the bushing and bring the bushing into yielding engagement with said pad, said coupling means also serving to limit relativeaxial movement of the bushing with respect to the hub and within said bushing and threadably engaging the hub-shaft assembly, said coupling serving to press said bushing and abrasive disk inwardly to a limited extent with respect to said pad to bring tween the back of the abrasive disk and the face of said pad.

7. A self-regulating friction drive for an abrasive disk employed in combination with a rotatabie shaft, comprising a hub secured to the shaft, a flexible pad apertured to fit loosely over the shaft and rest upon said hub, a sleeve nut engaging said shaft and having an integral flange adapted to press an abrasive disk upon said pad. and means carried by said nut for fixing the axial position of the nut on the shaft and thereby determining the degree of frictional engagement between the flange, disk, pad, and hub.

8. A tool comprising, a drive spindle having an end portion provided with a thread, a backing plate having a hub provided with a thread engagingthe thread on the spindle, a disk of pile fabric forming a pad positioned against a face of I thereof abutting against the abrasive surface of the abrasive disk said sleeve having a. smooth bore and being provided with an annular groove at the flanged end thereof adjacent the bore, a coupling sleeve extending through the bore oi' the friction sleeve and having an annular flange at one end thereof extending into the groove of the friction sleeve, said coupling sleeve having threaded engagement with the spindle providing 'for adjustment of the sleeve axially of the spindle whereby the friction sleeve can be adabrasive disk supported upon the pad and driv- I)usted toward the pad by the coupling sleeve and locking means for locking the coupling sleeve in adjusted position with respect to the spindle.

9. A tool comprising, a drive spindle, a backing plate having a hub attached to said spindle, a flexible pad positioned against a face of 'the backing plate and having a centrally located hole therein, concentric with the spindle, a flexible abrasive disk having a hole at the centre thereof with the non-abrasive side positioned against the pad, a friction sleeve extending through the holes in the abrasive disk and pad said sleeve having a ilange at one end thereof abutting against the abrasive surface of the abrasive disk, said sleeve having a. bore and being provided with an annular groove at the flanged end thereof adjacent the bore, a coupling sleeve extending through the bore of the friction sleeve and having an annular flange at one end thereof extending into the groove of the friction sleeve, said coupling sleeve having threaded coupling with said spindle and axial adjustment with respect to the spindle whereby the friction sleeve can be adjusted toward the pad by the coupling sleeve.

10. A disk driving device for a rotary sander having a rotatable shaft, comprising a pad mounted upon the shaft, an abrasive disk disposed upon the face of the pad, a bushing extending through the center of the disk and said pad and having an external flange engaging the surface of said disk, means including a threaded member frictionally engaging said. bushing and coupled mechanically to said shaft for transmitting driving torque from the shaft to said disk. and means for locking said threaded member in adjusted axial position with respect to said pad.

ROBERT DOUGLAS WATSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

